Sharpener for cutting blades



Feb. 16, 1960 R 5, FOX 2,924,918

SHARPENER FOR CUTTING BLADES Filed June 16, 1958 United States PatentSHARPENER FOR CUTTING BLADES Richard E. Fox, Northbro'ok, lll., assignorto Fox Howard Corporation, a corporation of Illinois Application June16, 1958, Serial No. 742,376 7 Claims. (Cl. 51-241) This inventionrelates to a sharpener for the cutting blades of power lawn mowers, andis particularly concerned with a grinding unit and means for detachablysecuring the grinding unit to the drive shaft of the gasoline engine ofa power lawn mower whereby it may be rotated by operation of the engine.

In accordance with the present invention, when the cutting blades of apower lawn mower become dull they may be removed and sharpened by meansof a grinding unit detachably mounted on the starter housing withoutsubstantial loss of time. The grinding unit may be kept permanently inits mounted position on the starter housing, if desired, but ispreferably removed from the starter housing when not being used, inorder to protect it from accidental damage during the normal use of themower.

Gasoline engines for power lawn mowers are usually provided with avertical drive shaft having cutting blades mounted on its lower end. Thepresent invention is particularly concerned with means for securing agrinding unit to a power lawn mower having a recoil starter. In mowersof this type the recoil starter is mounted in a housing secured to thetop of the engine housing and is engaged with the upper end of the driveshaft which projects through the top of the engine housing. The top ofthe starter housing is apertured, and the grinding unit includes a baseprovided with a depending stem which projects through the aperture ofthe starter housing into threaded engagement with an axial bore providedin the drive shaft of the engine. The base of the grinding unit has aplurality of circumferential cams on its vertical wall.

The grinding stone is in the form of a flat disc mounted in a frameadapted to seat on the base of the grinding unit. The upper face of thegrinding stone lies in a plane above the upper edge of the frame, andthe frame has a depending circular flange provided with inwardlyextending bosses engageable with the cams of the base to hold thegrinding stone in fixed relationship to the base.

The structure by means of which the above mentioned and other advantagesof the invention are attained will be described in the followingspecification, taken in conjunction with the accompanying drawings,showing a preferred illustrative embodiment of the invention, in which:

Figure 1 is a perspective view of a grinding unit mounted on top of arecoil starter for a gasoline engine in accordance with the invention;

Fig. 2 is a cross sectional view, taken along the line 2-2 of Fig. 1with parts of the starter mechanism omitted for clarity;

Fig. 3 is a top plan view of the base of the grinding unit;

Fig. 4 is a perspective view of the base of the grinding unit;

Fig. 5 is a bottom perspective view of the grinding stone and frame inwhich it is mounted; and

Fig. 6 is a bottom plan view of the frame for holding the grindingstone.

Referring to the drawings, the reference numeral 2 indiice cates agasoline engine for a power lawn mower. Engine 2 is mounted in a housinghaving a top wall 3 through which the upper end of the drive shaft 4projects. An axial bore Sis drilled into the upper end of drive shaft 4.A recoil starter 6 is mounted in a housing 7 having legs 8 secured totop wall 3 in any suitable manner. The top wall 9 of housing 7 has anaperture 10 aligned with axial bore 5. The gasoline engine and therecoil starter are conventional except for axial bore 5 and aperture 10,and therefore will not be specifically described. The purpose of axialbore 5 and aperture 10 will be hereinafter described.

The grinding unit, indicated generally by the reference numeral 11,comprises a grinding stone 12 mounted in a frame 13 which in turn issupported by a base 14. The grinding stone may be of any suitable shape,but preferably is in the form of a fiat cylindrical disc. Frame 13comprises a wall 15 having a horizontal cross sectional area conformingto the horizontal cross section of the lower surface of grinding stone12, and a vertical wall 16 conforming to the periphery of the grindingstone. Wall 15 is disposed intermediate the height of wall 16 to providean upstanding flange 17 and a depending skirt 18. Flange 17 preventslateral displacement of grinding stone 12 which is firmly held by wall15 and flange 17 in any suitable manner, as, for example, by adhesive.

Grinding stone 12 is thicker than the height of flange 17 and itsgrinding surface extends above the upper edge of the flange. Althoughthe grinding surface is preferably flat, it may have any desiredconfiguration. The lower edge portion of depending skirt 18 is providedwith circumferentially spaced inwardly extending bosses 19 for a purposehereinafter described. The number of bosses 19 may be varied, but theyare spaced uniformly of the circumference of the skirt regardless of thenumber provided. Each boss extends circumferentially of skirt 18 and theupper edges of the bosses are spaced uniformly from the underside ofwall 15.

Base 14 comprises a cup-shaped member 20 having a cylindrical wall 21adapted to fit within skirt 18 and a threaded stem 22. Stem 22 ispreferably in the form of a bolt adapted to engage the interior of axialbore 5. Bore 5 and stem 22 are threaded to interfit. Stem 22 extendsthrough an aperture 23 in the bottom 24 of the cup-shaped member 20 andis secured thereto by a flat washer 25 and a lock washer 26. Nuts 27 and28 are threaded on stem 22 to hold washers 25 and 26 in place. A lockwasher 29 is positioned on stem 22 between the top of drive shaft 4 andthe underside of nut 28. The washers 25, 26, 29 and nuts 27, 28cooperate with stem 22 to secure base 14 rigidly to drive shaft 4 and tothereby insure rotation of base 14 with the drive shaft.

The upper edge portion of wall 21 is provided with a series of cams 30extending in a general horizontal direction and embossed outwardly toprovide cam risers extending outwardly at right angles to wall 21. Cams30 are symmetrical and are spaced uniformly around the circumference ofbase member 14. The number of cams is the same as the number of bosses19 provided on skirt 18 and the spaces between the ends of adjacent camsis greater than the length of each boss 19. Frame 13 can be positionedon base 14 by dropping it vertically on the base, with bosses 19 passingvertically between cams 30 to seat the wall 15 on the upper edge of wall21.

The lowermost surface of each cam 30 is spaced from the upper edge ofwall 21 a distance greater than the space between the upper edge of eachboss 19 and the underside of wall 15. Accordingly, rotation of driveshaft 4 and base 14 will cause each cam 30 to interlock with one boss 19when frame 13 is seated on base 14. The interlocking engagement of frame13 with base 14 will the invention in considerabledetail,'itwillbe-understood' that the description'thereo'f is intended to be:illustrative,

rather than restrictive, as many details may be modified or changedwithout departingrfrom the spiritlor scope of" the invention.Accordingly, I do not desire to be" restricted to the exact constructiondescribed.

I claim:

1. In combination with. a lawn mowerengine having a vertical drive shaftand a threaded axial: bore" extending downwardly into the top of: said:drive shaft, a grinding unit comprising a base providedwith a dependingstein threaded to engage said axial bore, a frame mounted on said base,and a; grinding stonerigidly secured in: said frame.

2. Incombinatio'nwith a lawnmower engine having a vertical drive shaftanda threaded axial bore extending,

downwardly into the top of said drive shaft, a grinding unit comprisinga cup-shaped base provided with a plurality of outwardly extending camsand a depending stem threaded to engage said axial bore, a frame havingahorizontal wall and a vertical wall cooperating tosupport a grindingstone, said vertical wall havinglinwardly extending bosses engageablewith said cams to detachably secure said frame to saidbase.

3. In combination with a lawn mower engine having a vertical drive shaftand a threaded axial bore extending downwardly into the top of saiddrive shaft, agrinding unit comprising a cup-shaped base having. abottorn and a cylindrical vertical wall, a stern depending from saidbottom and threaded-to engage said axial bore, a plurality of outwardlyextending cams uniformly spaced circumferentially of said cylindricalwall, a frame having' a' circular skirt encircling said cylindricalwall, a plurality of bosses extending inwardly from said skirt, each ofsaid bosses t K 4 being of less length thanthe space betweenadjacent'cams, said bosses being spaced uniformly circumferentially ofsaid skirt, whereby said bosses may be passed through the spaces betweensaid cams and engaged with said cams to detachably secure said frame tosaid base, and a grinding stone rigidly secured in saidframe.

4. In combination with a power lawn mowerengine provided with a verticaldrive shaft, a grinding unit comprising a base, a frame, and a grindingstone rigidly secured' in said frame, said drive shaft having a threadedaxial bore extending downwardly into its upper end, said base having adepending stem and a series of cams, said stem being threaded to fit insaid axial bore, said frame being seated" on the upper edge of said baseand having a series of bosses adapted for interlocking engagement withsaid cams.

5. In combination with a power lawn mower engine provided with avertical drive shaft, a recoil starter engaging'sa'id drive shaft, ahousing enclosing said starter, said housing having a top wall having acentrally disposed aperture in alignment with the upper end of saiddrive shaft, a grinding unit comprisinga base, a frame, and a grindingstone rigidly secured in said frame, said drive shaft having a threadedaxial bore extending downwardly into its upper end, said base having adepending stem and a series of circumferentially spaced cams, said stembeing adapted to pass through said aperture and threaded to fit in saidaxial bore, said frame being'seated on the upper edge of said base andhaving a series of bosses adapted for interlocking engagement with saidcams; i

References Cited in the file of: this patent UNITED STATES PATENTS361,399 Davis Apr. 19, 1887 923,865 Lippincott Tune 8,v 1909 1,912,070Doermann May 30, 1933 2,841,931 Holzhansen et a1, July 8,. 1958 can

